Referring to FIGS. 1–2, an embodiment of a disc drive system 1 is shown that includes a disc drive unit 2, an actuator assembly 4 and a controller 6. The drive unit 2 includes a hard disc 8 and a shaft 10 connected to a drive motor 20. An actuator 12 receives input from the controller 6 to position a read/write head assembly 14 over the surface of the disc 8. A read/write head in the read/write head assembly 14 receives a sensing or bias current I from a current source 22. Variations in magnetization of the disc 8 cause changes in a magnetic field detected by the head assembly 14, which in turn results in a change in the electrical resistance of the read write head. This change in electrical resistance is detected with a readback circuit 24 that provides a data output 26. Referring to FIG. 3, the read/write head assembly 14 typically includes a slider 26 that flies above a surface of the disc 8. A read/write head 100 is located at or near the edge of the slider 26.
FIG. 4 is a cross-sectional view of a magnetic read/write head 100 and disc 8 taken along a plane normal to an air bearing surface 104 of the head 100. The air-bearing surface of the read/write head 100 faces a surface 106 of the disc 8, which travels or rotates in a direction relating to the head 100 as indicated by the arrow A. A write portion of the read/write head 100 includes a top pole 108 and a top shield 114, as well as multiple layers of conductive coils 112 that are held in place by an insulator layer 110. A read portion of the read/write head 100 includes the top shield 114, a top gap layer 115, a metal contact layer 116 a bottom gap layer 117, a bottom shield 118, and a giant magnetoresistive (GMR) stack 120. The top shield 114 functions both as a shield and as a shared pole for use with the top pole 108.
Referring to FIG. 5, a GMR stack 130 is shown that includes a ferromagnetic free layer 132, a tunnel barrier layer 134, a pinned layer 136, and an antiferromagnetic layer 138. A magnetization of the pinned layer 136 is fixed in a predetermined direction, generally normal to an air bearing surface 140 of the stack 130, while a magnetization of the free layer 132 rotates freely in response to an external magnetic field. The magnetization of the pinned layer 136 is pinned by exchange coupling pinned layer 136 with the antiferromagnetic layer 138. The resistance of the GMR stack 130 varies as a function of an angle formed between the magnetization of the pinned layer 136 and the magnetization of the free layer 132. The magnetization of the pinned layer 136 remains fixed in one direction, while the magnetization of the free layer 132 rotates in response to a fluctuating magnetic field emanating from the spinning magnetic media in the disc drive system. The angle formed between the magnetization of the free layer 132 and the magnetization of the pinned layer 136 changes in response to the fluctuating magnetic field emanating from the magnetic media, so the resistance of the GMR stack 130 also changes in response to this fluctuating magnetic field.